1. Field of the Invention
This invention relates to a method and apparatus for non-destructively measuring the moisture content in the inorganic coating of low hydrogen electric arc steel welding electrodes. More particularly, this invention relates to a low cost, light weight portable instrument suitable for field use, and to a method of using the instrument to determine the moisture content of welding electrodes.
A type of steel electric arc welding electrode commonly referred to as a "low hydrogen electrode" is used in some types of steel fabrication. For example, in the construction of off-shore well drilling and producing structures which are subject to heavy cyclical loadings, the use of these low hydrogen electrodes is often specified. Generally, the welds produced by these low hydrogen electrodes are less subject to hydrogen embrittlement. However, the inorganic coating portion of these low hydrogen electrodes must be free from moisture contamination in order to produce a sound weld. The maximum allowable moisture in the coating of a low hydrogen electrode is in the range of 0.02-0.5 percent by weight or in some cases even less.
2. Description of the Prior Art
The prevailing method of assuring that low hydrogen electrodes are sufficiently dry to be effective involves storing the electrodes in a sealed metal container until shortly before the electrodes are to be used. The containers in some cases are also stored in a heated environment to prevent accumulation of water. However, this method is not always successful as in some cases the containers develop leaks which enable an excessive amount of moisture to contaminate the normally hygroscopic inorganic coating of the welding electrodes. When the containers have once been opened, it is possible for moisture to accumulate rapidly on the unused welding electrodes in the container, as these welding electrodes are often used in areas having a high prevailing humidity, such as around shipyards.
There is no technique presently available for field use whereby the moisture content of a welding electrode can be accurately determined. The only methods previously avialable for determining moisture in welding electrode coatings involve laboratory procedures, such as set forth in American Welding Society Specification A.5.5-6.9; pages 25, 26 and 28. Alternative methods of welding electrode moisture measurement are discussed in "The Determination of Moisture in Electrode Coatings" by N. Jenkins and D. H. Parker -- Welding Institute Bulletin, Volume 14, Number 10, pages 291 through 295. These methods are not adaptable to field use.
Portable moisture testing instruments for measuring the moisture content of certain materials such as cereal grains, paper, tobacco, wood and soil by conductivity measurement have been used in the past. However, these portable instruments for moisture determination have all been low voltage instruments which are only suitable for use in determining the moisture content of a material which contains a relatively high amount of moisture, such as from 5 to 30 percent or more. U.S. Pat. Nos. 2,466,453; 2,461,111 and 2,582,629 are exemplary of such low voltage instruments for determining the moisture content of materials. Prior to this invention, there has been no portable instrument suitable for field use which could accurately determine the moisture content of a non-conductive solid such as the inorganic coating of a low hydrogen electric arc welding electrode where the range of moisture content of interest is a fraction of one percent by weight. Such a device is provided by this invention.